U.S. patent application number 12/528307 was filed with the patent office on 2010-12-23 for high throughput sem tool.
This patent application is currently assigned to APPLIED MATERIALS ISRAEL, LTD.. Invention is credited to Pavel Adamec, Gilad Almogy, Helmut Banzhof, Avishai Bartov, Jurgen Frosien.
Application Number | 20100320382 12/528307 |
Document ID | / |
Family ID | 46545551 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100320382 |
Kind Code |
A1 |
Almogy; Gilad ; et
al. |
December 23, 2010 |
HIGH THROUGHPUT SEM TOOL
Abstract
A multi-beam scanning electron beam device (100) is described.
The multi-bea scanning electron beam device having a column,
includes a multi-beam emitter (110) for emitting a plurality of
electron beams (12,13,14), at least one common electron beam
optical element (130) having a common opening for at least two of
the plurality of electron beams and being adapted for commonly
influencing at least two of the plurality of electron beams, at
least one individual electron beam optical element (140) for
individually influencing the plurality of electron beams, a common
objective lens assembly (150) for focusing the plurality of
electrons beams having a common excitation for focusing at least
two of the plurality of electron beams, and adapted for focusing
the plurality of electron beams onto a specimen (20) for generation
of a plurality of signal beams (121, 131,141), and a detection
assembly (170) for individually detecting each signal beam on a
corresponding detection element.
Inventors: |
Almogy; Gilad; (Kiriat Ono,
IL) ; Bartov; Avishai; (Hod-Hasharon, IL) ;
Frosien; Jurgen; (Ricmerling, DE) ; Adamec;
Pavel; (Haar, DE) ; Banzhof; Helmut; (Poing,
DE) |
Correspondence
Address: |
PATTERSON & SHERIDAN, L.L.P.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS ISRAEL,
LTD.
Rehovot
IL
|
Family ID: |
46545551 |
Appl. No.: |
12/528307 |
Filed: |
February 22, 2008 |
PCT Filed: |
February 22, 2008 |
PCT NO: |
PCT/EP2008/001413 |
371 Date: |
February 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60891185 |
Feb 22, 2007 |
|
|
|
61014702 |
Dec 18, 2007 |
|
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Current U.S.
Class: |
250/307 ;
250/311 |
Current CPC
Class: |
H01J 37/147 20130101;
H01J 37/05 20130101; H01J 2237/0635 20130101; H01J 2237/1508
20130101; H01J 37/10 20130101; H01J 2237/2817 20130101; H01J
2237/2449 20130101; H01J 37/28 20130101 |
Class at
Publication: |
250/307 ;
250/311 |
International
Class: |
G01N 23/00 20060101
G01N023/00; H01J 37/147 20060101 H01J037/147 |
Claims
1-24. (canceled)
25. A multi-beam scanning electron beam device having a column,
comprising: a multi-beam emitter for emitting a plurality of
electron beams; at least one common electron beam optical element
having a common opening for at least two of the plurality of
electron beams and being adapted for commonly influencing at least
two of the plurality of electron beams; at least one individual
electron beam optical element for individually influencing the
plurality of electron beams; a common objective lens assembly for
focusing the plurality of electron beams having a common excitation
for focusing at least two of the plurality of electron beams, and
being adapted for focusing the plurality of electron beams onto a
specimen for generation of a plurality of signal beams, wherein the
common objective lens has at least two openings for trespassing of
the plurality of electron beams; and a detection assembly for
individually detecting each signal beam on a corresponding
detection element.
26. The multi-beam scanning electron beam device according to claim
25, wherein the at least one common electron beam optical element
is a common beam separator with a common control for separating at
least two of the plurality of signal beams from the plurality of
electron beams.
27. The multi-beam scanning electron beam device according to claim
25, wherein the common electron beam optical element has one
opening for trespassing of at least two of the plurality of
electron beams or for trespassing of the plurality of electron
beams.
28. The multi-beam scanning electron beam device according to claim
26, wherein the common beam separator has one opening for
trespassing of the plurality of at least two of electron beams or
for trespassing of the plurality of electron beams.
29. The multi-beam scanning electron beam device according to claim
26, wherein the common beam separator is an achromatic beam
separator.
30. The multi-beam scanning electron beam device according to claim
26, wherein the achromatic beam separator is adapted for separating
the plurality of electron beams and the plurality of signal beams
without having a cross-over of the plurality of electron beams
and/or the plurality of signal beams for separation, in particular
inside the achromatic beam separator.
31. The multi-beam scanning electron beam device according to claim
26, further comprising a quadrupole generation element
superimposing the achromatic beam separator and adapted for
generation of a quadrupole field for correcting the deflection
angle of off-axis electron beams.
32. The multi-beam scanning electron beam device according to claim
25, further comprising: a double focusing beam bender, in
particular a hemispherical sector.
33. The multi-beam scanning electron beam device according to claim
32, wherein the double focusing beam bender has one opening for
trespassing of the plurality of beams.
34. The multi-beam scanning electron beam device according to claim
25, further comprising: a demagnifying or magnifying beam spacing
adapting optics.
35. The multi-beam scanning electron beam device according to
claims 25, wherein the common electron beam optical element is
selected from the group consisting of: an alignment element, a
stigmation corrector, a scanning element, and rotating element for
rotating the plurality of electron beams.
36. The multi-beam scanning electron beam device according to
claims 1, wherein the individual electron beam optical element is
selected from the group consisting of: a focusing element, a
stigmation corrector, an alignment element, a beam tilt introducing
element and a scanning element.
37. The multi-beam scanning electron beam device according to claim
25, wherein the beam spacing on the specimen between adjacent beams
is in a range of 0.5 to 5 mm, in particular 1.5 mm to 3.5 mm, more
particularly 2 mm to 3 mm.
38. The multi-beam scanning electron beam device according to claim
25 wherein the individual electron beam optical element is position
adjacent to or within the common objective lens assembly.
39. The multi-beam scanning electron beam device according to claim
25, wherein means for accelerating the plurality of electron beams
to high energies between the multi-beam emitter and the objective
lens, in particular to energies of 2 keV to 20 keV, and means for
decelerating the plurality of electron beams before impingement on
the specimen are provided.
40. The multi-beam scanning electron beam device according to claim
25, further comprising: focusing means for focusing each of the
plurality of signal beams on the corresponding detection
element.
41. The multi-beam scanning electron beam device according to claim
25, wherein multi-beam emitter is a spot grid array having
individual emitters for each of the plurality of electron
beams.
42. The multi-beam scanning electron beam device according to claim
25, wherein the device is adapted for avoiding a cross-over in the
column.
43. The multi-beam scanning electron beam device according to claim
25, wherein common objective lens assembly is an electrostatic lens
assembly, in particular in acceleration mode.
44. Method of operating a multi-beam scanning electron beam device
for generation of an image of a wafer including two or more dies,
comprising: scanning a first region of a first die of the two or
more dies for generating an image of the first region; scanning a
second region of a second die of the two or more dies for
generating an image of the second region; combining the image of
the first region and the image of the second region to an image of
a virtual die.
45. The method according to claim 20 wherein the virtual die is
combined by images of regions of three or four dies of the two or
more dies.
46. Method of operating a multi-beam scanning electron beam device
having at least a first and a second electron beam for generation
of an image of a wafer including at least one die, comprising:
scanning a non-overlap first region of the die with a first
electron beam current of the first electron beam for generating an
image of the first region; scanning a non-overlap second region of
the die with a second electron beam current of the second electron
beam for generating an image of the first region; scanning an
overlap region between a scanning area of the first and the second
electron beam with the first beam having a first overlap depending
beam current function having electron beam currents being smaller
than the first electron beam current and with the second beam
having a second overlap depending beam current function having
electron beam currents being smaller than the second electron beam
current.
47. The method according to claim 46, wherein the first current and
the second current are similar and the first overlap depending beam
current function and the second overlap depending beam current
function are similar.
48. The method according to claim 46, wherein the first and the
second overlap depending beam current functions are a linear
function.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a multi-beam electron
microscope, in particular a high throughput tool for the
semiconductor industry. Specifically it relates to a multi-beam
scanning electron beam device, a method of operating a multi-beam
scanning electron beam device, and uses of a multi-beam scanning
electron beam device.
BACKGROUND OF THE INVENTION
[0002] A modem semiconductor device is component of approximately
20-30 pattern layers that collectively implement the intended
functionality of the designer. In general, the designer describes
the chip functionality with high level, behavior design languages
like VHDL, and then a series of EDA tools translate the high-level
description into a GDSII file. The GDSII file contains a
geometrical description of polygons and other shapes that describe
the patterns of the different layers. The GDSII file accompanied
with process design rules for the fabrication process to be used to
make the device describes the intended geometry on the layout with
the relevant tolerances.
[0003] Modern photolithography presents several challenges,
including those associated with moving from 90 nm to 45 nm and 32
nm while keeping the stepper wavelengths at 193 nm. This requires
further transformation of the intended layout geometry to a post
resolution enhancement technique (RET) version of the GDSII file.
The new GDSII file includes pattern modifications for optical
proximity corrections (OPC) and mask technology. The complex set of
OPC corrections, mask-making and stepper conditions is required to
print the intended geometry on the wafer.
[0004] In light of the above, semiconductor technologies have
created a high demand for structuring and probing specimens within
the nanometer scale. Micrometer and nanometer scale process
control, inspection or structuring, is often done with charged
particle beams. Probing or structuring is often performed with
charged particle beams which are generated and focused in charged
particle beam devices. Examples of charged particle beam devices
are electron microscopes, electron beam pattern generators, ion
microscopes as well as ion beam pattern generators. Charged
particle beams, in particular electron beams, offer superior
spatial resolution compared to photon beams, due to their short
wavelengths at comparable particle energy.
[0005] For semiconductor manufacturing, throughput can be a
significant limitation in tools for scanning a geometry in its
entirety. Assuming a CD-SEM resolution of 1 nm, a 10 mm.sup.2 die
contains 10E14 pixels. Accordingly, for covering the entire layout,
a parallel architecture is desired.
[0006] Electron beam systems for multiple electron beams, which may
be used for a fast wafer inspection, are generally realized by
either an array of conventional single beam columns having a
spacing in the range of a few centimeters or by a single column
with an array of beams. In the latter case, the beam array has
relatively small electron beam spacing in a range of 10 .mu.m-100
.mu.m. Thereby, a high number such as hundreds or even thousands of
beams can be used. However, individual corrections of the beams are
difficult.
[0007] In order to provide a tool that utilizes electron beam
optics to scan the entire geometry of the chip layer within
resolution and desired signal to noise ratio (SNR), which enables
extraction and verification of the wafer pattern geometry against
the design-intended GDSII file, i.e. the original GDSII file,
improved and different system designs have to be considered.
SUMMARY
[0008] In light of the above, a multi-beam scanning electron
microscope according to independent claim 1, a method of operating
a multi-beam scanning electron beam device according to independent
claims 12 and 13 are provided.
[0009] According to one embodiment, a multi-beam scanning electron
beam device is provided. The multi-beam scanning electron beam
device having a column, includes a multi-beam emitter for emitting
a plurality of electron beams, at least one common electron beam
optical element having a common opening for at least two of the
plurality of electron beams and being adapted for commonly
influencing at least two of the plurality of electron beams, at
least one individual electron beam optical element for individually
influencing the plurality of electron beams, a common objective
lens assembly for focusing the plurality of electron beams having a
common excitation for focusing at least two of the plurality of
electron beams, and being adapted for focusing the plurality of
electron beams onto a specimen for generation of a plurality of
signal beams, and a detection assembly for individually detecting
each signal beam on a corresponding detection element.
[0010] Further advantages, features, aspects and details that can
be combined with embodiments described herein are evident from the
depending claims, the description and the drawings.
[0011] According to another embodiment, a method of operating a
multi-beam scanning electron beam device for generation of an image
of a wafer including two or more dies is provided. The method
includes scanning a first region of a first die of the two or more
dies for generating an image of the first region, scanning a second
region of a second die of the two or more dies for generating an
image of the second region, and combining the image of the first
region and the image of the second region to an image of a virtual
die.
[0012] According to yet another embodiment, a method of operating a
multi-beam scanning electron beam device having at least a first
and a second electron beam for generation of an image of a wafer
including at least one die is provided. The method includes
scanning a non-overlap first region of the die with a first
electron beam current of the first electron beam for generating an
image of the first region, scanning a non-overlap second region of
the die with a second electron beam current of the second electron
beam for generating an image of the first region, and scanning an
overlap region between a scanning area of the first and the second
electron beam with the first beam having a first overlap depending
beam current function having electron beam currents being smaller
than the first electron beam current and with the second beam
having an second overlap depending beam current function having
electron beam currents being smaller than the second electron beam
current.
[0013] Embodiments are also directed to apparatuses for carrying
out the disclosed methods and including apparatus parts for
performing each described method step. These method steps may be
performed by way of hardware components, a computer programmed by
appropriate software, by any combination of the two or in any other
manner. Furthermore, embodiments according to the invention are
also directed to methods by which the described apparatus operates.
It includes method steps for carrying out every function of the
apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments. The accompanying drawings
relate to embodiments of the invention and are described in the
following:
[0015] FIG. 1 shows a schematic view of a multi-beam scanning
electron beam device according to embodiments described herein;
[0016] FIG. 2A shows a schematic view of an achromatic beam
separator for multi-beam scanning electron beam devices according
to embodiments described herein;
[0017] FIG. 2B shows another schematic view of an achromatic beam
separator for multi-beam scanning electron beam devices according
to embodiments described herein;
[0018] FIG. 2C shows a schematic enlarged view of an achromatic
beam separator and an off-axis correction thereof according to
embodiments described herein;
[0019] FIG. 2D shows a schematic enlarged view of an achromatic
beam separator and a further off-axis correction thereof according
to embodiments described herein;
[0020] FIGS. 3A to 3E show results of model simulations for an
achromatic beam separator according to embodiments described
herein;
[0021] FIG. 4 shows a schematic view of a detection scheme for
multi-beam scanning electron beam devices according to embodiments
described herein;
[0022] FIGS. 5A and 5B illustrate scanning schemes that can be used
for multi-beam scanning electron beam devices according to
embodiments described herein;
[0023] FIG. 6 illustrates a further scanning scheme that can be
used for multi-beam scanning electron beam devices according to
embodiments described herein;
[0024] FIG. 7 shows a schematic view of a further multi-beam
scanning electron beam device according to embodiments described
herein;
[0025] FIG. 8 shows a schematic view of a further multi-beam
scanning electron beam device according to embodiments described
herein;
[0026] FIG. 9 shows a schematic view of yet a further multi-beam
scanning electron beam device according to embodiments described
herein;
[0027] FIG. 10 shows a schematic view of an even further multi-beam
scanning electron beam device according to embodiments described
herein;
[0028] FIGS. 11A to 11C show schematic views of multi-beam emitters
usable for multi-beam scanning electron beam devices according to
embodiments described herein; and
[0029] FIG. 12 shows a schematic view of a primary beam path of a
further multi-beam scanning electron beam device according to
embodiments described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Reference will now be made in detail to the various
embodiments of the invention, one or more examples of which are
illustrated in the figures. Each example is provided by way of
explanation of the invention and is not meant as a limitation of
the invention. For example, features illustrated or described as
part of one embodiment can be used on or in conjunction with other
embodiments to yield yet a further embodiment. It is intended that
the present invention includes such modifications and
variations.
[0031] Without limiting the scope of protection of the present
application, in the following the charged particle beam device or
components thereof will exemplarily be referred to as a charged
particle beam device including the detection of secondary
electrons. The present invention can still be applied for
apparatuses and components detecting corpuscles such as secondary
and/or backscattered charged particles in the form of electrons or
ions, photons, X-rays or other signals in order to obtain a
specimen image.
[0032] Generally, when referring to corpuscles it is to be
understood as a light signal, in which the corpuscles are photons,
as well as particles, in which the corpuscles are ions, atoms,
electrons or other particles.
[0033] Within the following description of the drawings, the same
reference numbers refer to the same components. Generally, only the
differences with respect to the individual embodiments are
described.
[0034] A "specimen" as referred to herein, includes, but is not
limited to, semiconductor wafers, semiconductor workpieces, and
other workpieces such as memory disks and the like. Embodiments of
the invention may be applied to any workpiece on which material is
deposited, which is inspected or which is structured. A specimen
includes a surface to be structured or on which layers are
deposited, an edge, and typically a bevel.
[0035] For ease of reference, the term "common" as used herein is
generally understood as referring to elements acting commonly on
two or more beams, e.g., all beams, in the multi-beam system. The
term "individual" as used herein is generally understood as
referring to elements acting on individual beams only such that the
individual beams can be independently controlled, modified,
influenced or the like.
[0036] According to embodiments described herein, a multi-beam
system with beam spacing that allows to separate between secondary
beams (signal beams) without further restrictions, that allows for
individual as well as common beam corrections, deflections,
adjustment and/or focusing, and/or that allows the size of beam
array not to be bigger than a few dies, e.g., one, two or three
dies, in order to allow simultaneous inspection of the same die or
neighboring dies is provided. Thereby, according to typical
embodiments, in particular a high throughput multi-beam CD-SEM tool
can be provided.
[0037] The multi-beam scanning electron microscope includes a
multi-beam emitter 110. As sown in FIG. 1, the emitter tip 102 of
the multi-beam emitter 110 emits an electron beam as indicated by
the dashed lines. The aperture plate 106 of the
multi-electron-emitter 106 generates electron beams 12, 13 and 14
respectively. Embodiments described herein are not limited to a
line of three electron beams. According to further embodiments,
lines of 2 to 10 or even 20 electron beams or more as well as
arrays having from 2 to 10 or even 20 electron beams or more in one
dimension of the array can be realized.
[0038] The multi-beam scanning electron beam device 100 includes
common electron beam optics 120. A common electron beam optical
element acts simultaneously on more than one, e.g., all of the
electron beams (e.g. electron beams 12, 13 and 14 in FIG. 1.) The
common electron beam optics can be selected from the group
consisting of: condenser lenses (see, e.g. 120 in FIG. 1),
alignment deflectors, field stigmators, and scanning deflectors. As
a further example, it might be a rotation lens for rotating the
line or array of electron beams. Thereby, as a typical
implementation, two or more electron beams can pass through the
same opening of the common electron beam optical element, e.g. the
same opening for trespassing of the beam in the condenser lens 120
shown in the multi-beam emitter 110.
[0039] Further, the multi-beam scanning electron beam device 100
includes individual beam optics 140, which can be selected from the
group consisting of: scanning deflectors, stigmators, individual
focus adjustment units or individual focusing units for adjusting
the individual focus of the electron beams.
[0040] According to additional or alternative implementations, the
individual electron beam optics may be a pre-lens octupole system
for individual beam alignment, beam scanning, lens alignment,
stigmation correction and adjustment of individual focusing.
[0041] According to embodiments described herein, the multi-beam
scanning electron beam device 100 further includes a common lens
assembly 150 being an objective lens and focusing the line or array
of electron beams simultaneously. The common objective lens
assembly 150 can be electrostatic, magnetic or combined
electrostatic-magnetic.
[0042] According to further additional or alternative
implementations of the objective lens assembly, the array lens can
be an electrostatic lens array, typically in an acceleration mode,
a magnetic lens array or a combined electrostatic-magnetic lens
array. If according to yet further embodiments, which can be
combined with other embodiments described herein, at least a
scanning element is close to the front focal plane of the objective
lens assembly, telecentricity can be improved.
[0043] Yet further, the multi-beam scanning electron beam device
includes a detection assembly 170 with a detection element
corresponding to each individual beam. Accordingly, as shown in
FIG. 1, there is one detection element for detecting secondary
and/or backscattered particles for each of the electron beams 12,
13, and 14, respectively.
[0044] FIG. 1 shows an example of a multi-beam high throughput
tool. Features of the multi-beam scanning electron beam device 100
can include a high current, high-resolution SEM, no
electron-electron interaction in light of separated beams,
individual scan, fine focus and stigmation correction for the
individual beams, a high telecentricity in light of the position of
the scanner in front of the focal plane, for example, an
electronics and the detector at ground potential, separate
detection elements for each beam, e.g. scintillator fiber detection
with subsequence multipliers, and a scalability starting from a
4.times.4 array to a 10.times.10 array and beyond.
[0045] In the past, systems having the beam spacing that allows to
separate between secondary beams without significant restrictions
and at the same time having a beam spacing such that the array is
not bigger than 1, 2 or 3 dies for a simultaneous inspection of the
same die or neighboring dies have not been highlighted. According
to embodiments described herein, multi-beam scanning electron beam
devices can be provided and have a typical distance between two
adjacent beams of a line of beams or an array of beams in the range
of 0.5 to 5 mm, typically 1.5 to 3.5 mm, for example, 2 to 3 mm.
Accordingly, embodiments described herein may include common
electron beam optics, individual electron beam optics, common
objective lens systems and individual detection, wherein for
example also a separation between the beams to be detected can be
conducted in an improved manner.
[0046] According to some embodiments described herein, as for
example shown in FIG. 1, the multi-beam scanning electron beam
device 100 may have a multi-beam emitter 110 including a single
emitter tip 102, one or more elements for extracting, accelerating
and/or shaping the electron beams and a grid aperture 106 for
generating individual electron beams. Thereby, the emitter tip 102
of the multi-beam emitter emits one beam which is serparated into
the multiple beams by the aperture 106 of the multi-beam emitter
110. According to other embodiments, an emitter array with
individual emitters for each electron beam can be used According to
yet other embodiments, a spot grid array, wherein the emission of
one emitter tip is shaped and formed to exit in parallel and as
corrected beams can also be used. Thereby, the grid aperture array
or two or more grid aperture arrays can be used at one ore more
potentials in order to shape and/or focus the beam. Accordingly,
the emission of one emitter can appear in the column as multiple
sources. Thus, subsequent optical elements or in combination with
subsequent optical elements the multiple beams at the specimen
appear to be generated by multiple sources. In light of the above,
on the one hand, two or more emitters can be used for generation of
the multiple beams. On the other hand, one emitter can be used.
Thereby, one source or two or more sources can be provided by the
one emitter.
[0047] According to yet further embodiments, the multi-beam
emitter, i.e. the gun condenser area, can be provided as follows.
According to one embodiment, a single emitter electron gun,
typically the TFE source can be used. The aperture array for
multi-beam generation can be included in an upper part of the
column for generating the individual electron beams as early as
possible. Thereby, the total beam current can be reduced as early
as possible for avoiding electron-electron interaction. Thus, the
overall current is reduced as early as possible in the column by
generating the beamlets out of the common beam. According to yet
further embodiments, the condenser for adjusting the virtual source
z-location (z denoting the optical axis) and/or for matching the
aperture array with the objective lens array can be included.
According to yet further alternative or additional modifications,
an X-Y stage for the aperture array can be provided in order to
align the apertures for individual beam generation to the objective
lens array. Typically, it is for example possible to have an
electro-magnetic alignment. According to even further additional or
alternative modifications the mechanical aperture stage can be
rotated or an axial magnetic field for rotation adjustment of the
apertures to the objective lens array can be provided.
[0048] According to yet other embodiments, which can be combined
with any of the embodiments described herein, a common achromatic
deflector 130 or common achromatic beam separator 130 having an
electrostatic deflection element 132 and the magnetic deflection
element 134 can be provided. Within FIG. 1, only the magnetic field
is indicated for illustrating the magnetic deflection element. The
achromatic deflector 130 will be described in more detail with
respect to the FIGS. 2A and 2B below. The achromatic deflector 130
deflects the primary electron beams 12, 13 and 14, respectively (in
FIG. 1) and separates the primary electron beams 12, 13 and 14 from
the secondary electron beams, i.e., the signal beams 12', 13', and
14'. A double focusing bender 160 provides further beam separation.
Details of further embodiments relating to the double focusing
bender will be described with respect to FIG. 4 below.
[0049] FIG. 2A shows an enlarged view of the achromatic separator.
State of the art electron beam devices mostly use magnetic
deflectors or Wien filters for beam separation of primary and
secondary beams. Thereby, substantially perpendicular static
electric and magnetic fields normal to the z-axis (optical axis)
are used. The force acting on the electrons is given by the coulomb
force
F.sub.e=qE (1)
[0050] and the Lorentz force
F.sub.n=q(v.times.B) (2)
[0051] The angle of deflection of the electrons in the electric and
magnetic fields, both of length l, can be described with the
following equation:
.theta.=ql(vB-E)/(mv.sup.2) (3)
[0052] FIG. 2A illustrates one embodiment of an achromatic bender
or achromatic beam splitter 130. Therein, coil windings 163 and
plate-shaped electrodes 165 are shown. The coils 163 generate a
magnetic field 31. The magnetic field generates a magnetic force 32
for an electron beam 170. The magnetic force is generated according
to equation 2. Substantially perpendicular to the magnetic field 31
an electric field is generated between the electrodes 165. Thereby,
an electric force 33, which is substantially opposite to the
magnetic force, is generated.
[0053] The embodiment shown in FIG. 2A generates perpendicular,
uniform magnetic and electric fields. Within FIG. 2A, the electron
beam path 170 is slightly inclined with respect to the axis 142
when the electrons enter the achromatic deflector. The electrons
are deflected within the achromatic deflector to travel essentially
along axis 144 after trespassing the achromatic deflector. This can
be understood in light of the derivative of equation 3, that is
d.theta./dv=-(qlB/mv.sup.2)(1-2E/vB) (4)
[0054] The deflection angle is independent of the velocity of the
electrons if the condition that the magnetic force equals twice the
electric force is fulfilled. In FIG. 2A this is illustrated by the
lengths of the force indicating arrows 32 and 33.
[0055] In embodiments described herein, the achromatic deflector
162 can be described at least by one of the following features.
According to one embodiment, 20 to 80 ampere turns (Aturns), e.g.,
40 Aturnes may be provided. According to an even further
embodiment, about 10 to 400 coil windings can be provided. Yet
according to another embodiment, 50 to 500 coil windings can be
provided. Nevertheless, it might be possible to provide even more
coil windings, for example, up to a few thousand.
[0056] According to an even further embodiment, the achromatic
deflection angle can be between 0.3.degree. and 7.degree..
According to another further embodiment, the deflection angle is
between 1.degree. and 3.degree..
[0057] The achromatic beam deflector or beam splitter shown in FIG.
2A can be used in accordance with the present invention. Thereby,
as described above, electrostatic deflection is given by:
.alpha. e .varies. E 1 U A , U A .fwdarw. U A + .DELTA. U A
.delta..alpha. .varies. - .DELTA. U A ##EQU00001##
[0058] Further, magnetic deflection is given by:
.alpha. m .varies. B 1 U A , U A .fwdarw. U A + .DELTA. U A
.delta..alpha. .varies. - 1 2 .DELTA. U A ##EQU00002##
[0059] As described above, if the magnetic deflection equals minus
two times the electrostatic deflection a deflection without
chromatic aberration (dispersion) can be realized.
[0060] According to some embodiments described herein, which are
illustrated with respect to FIG. 2B, systems including
substantially pure dipole fields can be used. FIG. 2B shows a
system having eight electrodes and pole pieces. Cores 564 are
connected to the housing 566 via insulators 563. The coils for
exciting the cores and, thereby, the pole pieces are wound around
the cores 564. At the other end of the cores, electrode-pole pieces
567/8 are provided. According to embodiments employing a deflection
unit as, for example, shown in FIG. 2A, the fringing fields can be
provided to be similar for the magnetic field and the electric
field; and highly pure dipole fields can be generated. However, the
system including eight coils and eight electrodes require more
current- and voltage-sources, thereby, costs are increased. As a
result, optimized systems having two poles each (electric and
magnetic), might typically be used for the embodiments described
herein.
[0061] Generally, embodiments described herein relate to a high
throughput, high-resolution imaging system. The imaging system
(multi-beam scanning electron beam device) may include a multi-beam
system with a high-performance objective lens array with low
spherical and chromatic aberration, a low operation beams separator
for separating primary and secondary electron beams, and a
multi-channel signal detection.
[0062] As shown in FIG. 2C, if according to some embodiments the
electron beams do not enter the common achromatic beam separator
parallel to each other the above described achromatic condition
might not be fulfilled for all electron beams. FIG. 2C shows three
electron beams entering the achromatic beam separator 130 having an
electrostatic deflection element 132 and magnetic deflection
elements 134. Thereby, the center beam is shown to meet the above
described achromatic condition. However, the other two electron
beams have a tilt angle which is different from the center electron
beam and which is indicated with regard to the optical axis 2 of
the objective lens assembly 150 and the tilted axis 4 and 4',
respectively. Accordingly, for non-parallel electron beams the
achromatic beam separator is not perfectly achromatic for all of
the electron beams and can thus be denoted as a low aberration
beams separator.
[0063] According to some embodiments, as shown in FIG. 2C, the
individual electron beam optics 140 can be provided in the form of
a quadrupole element or the like. Thereby, the beam tilt indicated
by axis 4 and 4' of the left electron beam and the right electron
beam, respectively, which is not parallel to the center electron
beam, which has been deflected achromatically, can be introduced in
the individual electron beam optics 140. The beam tilt
-.alpha..sub.tilt and .alpha..sub.tilt, which is introduced for
vertical landing and alignment to the objective lens can thereby be
introduced. Accordingly the individual electron beams pass through
the common objective lens assembly 150 in parallel after
compensating the off-axis electron beams.
[0064] According to further embodiments, as shown in FIG. 2D, the
achromatic beam separator 130' having an electrostatic deflection
element 132' and the magnetic deflection element 134' can be
compensated by a superimposed quadrupole field, provided by
quadrupole elements, which adjusts the achromatic beam deflection
for electron beams that do not pass through the achromatic beam
separator 130' on the center axis. As shown with respect to FIG.
2B, the achromatic beam deflector can be realized by an octupole
element. This octupole element allows for an adjusted beam
deflection for electron beams that travel through the achromatic
beam separator off-axis. Thereby, the electron beams exit the
achromatic beam separator parallel, as shown in FIG. 2D and
dispersion of beam tilt deflectors such as element 140 can be
avoided.
[0065] According to some embodiments, the multi-beam scanning
electron microscope can have a common beam bender (see, e.g., 160
in FIG. 1) adapted for having several electron beams trespassing
therethrough. After the primary beams are focused on the specimen,
the beams of primary charged particles undergoes different
interactions with the specimen resulting in secondary particles
wherein, the term "secondary particles" is to be understood as
including all particles leaving the specimen. Those secondary
particle beams (see, e.g., 12'; 13' and 14' in FIG. 1) that go
through the deflector 130, and which are for example accelerated
towards the deflector 130, are deflected towards the beam bender
160.
[0066] Generally, beam benders such as bending sectors that might
be combined with the embodiments disclosed herein might be
electrostatic, magnetic or combined electrostatic-magnetic. Since
the space required for an electrostatic bending sector is smaller
than the space needed for a sector including a magnetic part,
typically an electrostatic sector is used. An electrostatic bending
sector may be two electrodes which are shaped roundly. The sector
may have a negatively-charged electrode and a positively-charged
electrode serving to bend the electron beam. Thereby, the electron
beam is focused in one dimension and, additionally, is kept at a
high energy to avoid time of flight effects which may have impact
on a high-speed detection. A focusing in the second dimension can
take place in a quadrupole element, by an electrostatic side plate
or a cylinder lens. Thereby, a double-focusing bender, e.g. in the
form of a double-focusing sector unit can be provided.
[0067] Thereby, the beam of secondary charged particles can be
deflected by about 90.degree. with respect to the beam of primary
charged particles. However, other values between 30.degree. and
110.degree., typically between 45.degree. and 95.degree. or between
60.degree. and 85.degree., are also possible. Additional to the
deflection, the beam is typically also focused, as described above
already. One advantage of applying a bending sector is that the
beam of secondary charged particles is guided away from the direct
vicinity of the primary charged particle beam. Thus, analysis tools
can be applied in the charged particle beam device without the need
to fit them into the limited space nearby the primary charged
particle beam and furthermore, without leading to undesirable
interactions with the primary charged particle beam.
[0068] Instead of the electrodes, which may optionally be provided
with additional side plates, the bending sector can be a
hemispherical sector. The hemispherical sector allows for the
two-dimensional focusing of the beam. Thus, no additional focusing
unit is required for a double focusing sector unit. Generally, an
electrostatic beam bending sector can be either cylindrical or
hemispherical. The cylindrical type suffers from the fact that as
the beam is bent the secondary electrons are focused in one plane
and not in the other. A hemispherical bending sector focuses the
secondary beam in both planes. The cylindrical sector can be used
with side plates biased to achieve focusing in the transverse
plane, yielding similar focusing properties to the hemispherical
sector.
[0069] A model of an achromatic beam separation or beam deflector,
which may also be used as an embodiment, which can be combined with
other embodiments described herein, can be described as follows.
Saddle coils having an inner diameter of 36 mm and a 2 mm.times.2
millimeter X-section, as well as 40 ampere turns, may further have
a length of about 30 mm. A 60.degree. angle of the saddle coils can
reduce or avoid hexapole components. Further, alternatively, a
combination of coils with a 42.degree. and 78.degree. angle can
reduce or avoid hexapole and decapole components. The electrostatic
deflector, i.e. the electrodes shown in FIG. 2B, may have an
optical geometry of an inner diameter of 16 mm and a length of 30
mm Further, a +-500 V deflection voltage (static) floating on
column voltage can be provided. If, as described with respect to
FIG. 2B, x,y,=0.7071X,Y, hexapole and decapole components may be
reduced or avoided. For the model, the column voltage is given as
9.5 keV, that is the, voltage can in general be set on increased
potential (e.g., 5 times, 10 times or even 20 times increase) for
providing the beam boost within the column, and the landing energy
is 500 eV or 1 keV, respectively.
[0070] FIG. 3A presents a simulation result of the beam separator.
The deflection causes some astigmatism. However, the astigmatism is
small enough to be corrected. The corrected astigmatism is shown in
FIG. 3B. Thereby, the spot diameter can be reduced from 24 nm in
FIG. 3A to about 1 nm in FIG. 3B. FIGS. 3C and 3D further show that
the achromatic beam separator or achromatic beam deflector, which
has been described above, does not introduce additional chromatic
aberrations. Thereby, FIG. 3C shows the spots without the beam
separator, wherein FIG. 3D shows the spots with a beam separator.
In the FIGS. 3C and 3D no substantial difference can be seen. FIG.
3E shows a further simulation of the beam separator showing large
beam X-sections with a 60.degree. saddle coil. As can be seen in
FIG. 3E, no significant additional aberrations, for example
"hexapole" coma, are introduced. Accordingly, a 60.degree. saddle
coil with large diameter can be considered sufficient for
embodiments of an achromatic or low aberration beam separator as
described herein.
[0071] As can be shown by simulations, the achromatic beam
deflector is also not very sensitive to energy changes of the
landing energy on the specimen. Thus, the tolerance with respect to
the change of energy can be reduced for smaller deflections. The
deflector does not need to be readjusted for small energy
variations.
[0072] Further alternative or additional implementations with
regard to the detection that might for example include a
spectrometer, will now be described. Thereby, reference will partly
be made to FIG. 4. Generally, the achromatic beam separator might
be considered achromatic for the primary electron beams but may
introduce dispersion for the secondary signal beams. For easier
understanding, FIG. 4 shows only one primary and one signal beam.
However, the same principle can be used for a plurality of signal
beams.
[0073] The achromatic beam deflector separates the signal beam from
the primary beam and introduces a dispersion as indicated by the
three different beams. After trespassing the beam bender, e.g., in
form of a sector, the dispersion can be seen in the plane of a
dispersive image indicated by reference numeral 474. The lens 472
images the different virtual images corresponding to different
signal beam energies on the sub-detection elements 471. Thereby,
energy filtering can be realized.
[0074] The beam rays of the center beam is indicated in FIG. 4. As
can be seen there is a crossover shortly after the bending sector
160. Generally, according to other embodiments, the sub-detection
elements may also be positioned directly after the bender 160,
typically in the focus of the different signal beams having
different signal energies. However, the lens 472 allows for imaging
and magnification of the energy spread. Accordingly, a fast and
parallel detection of different .DELTA.E channels can be realized.
This might for example be used for element mapping or potential
mapping, e.g., for dopant profiles.
[0075] If a multi-beam system is used, a further sub-detection
element array can be provided adjacent to the sub-detection
elements 471 shown in FIG. 4.
[0076] According to other embodiments, the use of a multi-beam
scanning electron system and method of operating multi-beam
scanning electron systems according to embodiments described herein
are provided. Generally a 2-D array of scanning electron beams is
provided, thereby, typically each electron beam has the resolution
performance similar to a single beam device, for example a CD-SEM.
In the array, each beam scans a few square microns and the overall
throughput is the multiplication of a single beam throughput with
the number of beams.
[0077] Generally, a wafer to be inspected is positioned in the tool
on an XY-stage. According to some embodiments, which can be
combined with other embodiments described herein, scanning is done
in the step and scan manner. Thereby, during scanning the stage is
not moved and waits until the current frame scanning is completed.
When the scanning of the frame is finished the stage travels to the
next frame location.
[0078] One major problem for multi-beam scanning electron beam
devices is the beam overlap within such high throughput systems
because a significant part of the surface may lie within two beams.
Thereby an overlap of the scanning area of two adjacent beams is
provided. This overlap is generally problematic for electron beam
imaging as the overlap region will suffer from a different charging
regime, in particular if scanning of overlapping regions is
conducted within a short time period.
[0079] According to different embodiments, which might be combined
with each other, an improved scanning is provided. According to one
alternative, a combined scan can be provided. Generally for a
design for manufacturing (DFM) die to database scanning, systematic
defects should be detected. Accordingly, according to some
embodiments described herein, it is possible to deduce the
inspection result from a virtual die image Thereby, a virtual die
image can include portions of several physical dies. The virtual
die image can be built in a way that will not require overlaps
between beams on the array, in particular not within a time period
that is sufficient in order to have previously charge been
degraded. The first option is a rectangular scanning scheme wherein
portions of four different dies are scanned in order to generate
one virtual die image. As shown in FIG. 5A, each of the portions 1,
2, 3 and 4 are portions of two or more (up to four) physical dies.
These images are combined to form a virtual die 504 image which is
used for inspection purposes.
[0080] FIG. 5B shows a hexagonal scanning scheme, which includes
scanning of three different portions 502 of different dies in order
to form a virtual die image, which can be used for inspection
purposes. The overlap 503 shown in FIG. 5B has no negative effect
since the scanning of a physically neighboring region can be
conducted after a charge of the respective specimen region has
sufficiently disappeared.
[0081] According to another embodiment, a trapezoid current
profile, as shown in FIG. 6, can be used for the beam current of
the individual electron beams. Thereby also a single die can be
scanned. It is assumed that the beam overlay effect can be reduced
significantly by a scanning scheme that will ensure an overall
current density in the overlap region 604 that is equal to the
current density in the non-overlap regions 602. If, as an example,
the beams are placed in a regular rectangular grid and the
scattering amplitude is larger than the periodicity of the grid, an
overlap is created.
[0082] According to some embodiments, which can be combined with
other embodiments described herein, the overlap regions 604 are
scanned as follows: In the scanning direction, which is denoted as
the X-direction, the current profile is a trapezoid, wherein the
cap (602) of the trapezoid corresponds to the single beam region
602 and the beam current of the respective electron beams decreases
linearly along the overlapping region 604. Thereby, the total
current in the overlap region 604 is equal to the current in the
cap region of the trapezoid, where only a single beam is used.
[0083] Further, for the Y-axis the lines scanned in the X-direction
will have a line current that will be modulated in a similar
manner. The overlap image signal can be detected in parallel on
those two beam detectors, which correspond to the two electron
beams generating the overlap.
[0084] According to optional implementations, image processing
techniques which can for example be based on interpolations, will
be applied to recombine the two images. Thereby an image quality of
the combined image can be similar or close to the image quality in
the single beam regions.
[0085] As for example shown in FIG. 7, according to further
embodiments, which might be combined with other embodiments
described herein, a multi-beam scanning electron beam device can be
provided as follows. In FIG. 7, the beam generation is not shown.
The beams can for example be generated by an array of individual
emitters or a single emitter. Alternatively, they can be generated
by a grid aperture array, a grid lens array, a combination thereof
and/or a grid aperture array and a lens. Thus, according to some
embodiments described herein, as for example shown in FIG. 1, the
multi-beam scanning electron beam device 100 may have a multi-beam
emitter 110 including a single emitter tip 102, one or more
elements for extracting, accelerating and/or shaping the electron
beams and a grid aperture 106 for generating individual electron
beams. According to other embodiments, an emitter array with
individual emitters for each electron beam can be used. According
to yet other embodiments, or a spot grid array, wherein the
emission of one emitter tip is shaped and formed to exit in
parallel and as corrected beams can also be used. Thereby, the grid
aperture array or two or more grid aperture arrays can be used at
one ore more potentials in order to shape and/or focus the beam.
Accordingly, the emission of one emitter can appear in the column
as multiple sources. Thus, subsequent optical elements or in
combination with subsequent optical elements the multiple beams at
the specimen appear to be generated by multiple sources. In light
of the above, on the one hand, two or more emitters can be used for
generation of the multiple beams. On the other hand, one emitter
can be used. Thereby, one source or two or more sources can be
provided by the one emitter.
[0086] The beams 12, 13 and 14, respectively pass first through
individual electron beam optics 140 which can for example include
lenses, multi-poles and the like. At this position in the electron
beam column, the individual electron beams have a relatively large
distance with respect to each other. The distance of the individual
beams with respect to each other can according to some embodiments
be reduced by an adapting optics having a first lens 725 and the
second lens 727. As shown in FIG. 7, a demagnifying adapting optics
can be provided. Thereby, the distance of the electron beams with
respect to each other can be reduced. Thereafter, according to some
embodiments, which can be combined with other embodiments described
herein, the distance between adjacent beams can be in a range of
1.5-3.5 mm, typically 2-3 mm. The plurality of electron beams is
further influenced by common electron beam optics 120 such as a
beam corrector 722 and a common deflection system 724. A common
objective lens array focuses the plurality of electron beams on the
specimen 20. Thereby, a magnetic objective lens component 752 and
an electrostatic lens component 754 having one or more electrode
plates can be used. Accordingly, a common objective lens assembly
150 is provided.
[0087] Accordingly, for some embodiments described herein, a
magnifying or demagnifying adapting optics for adapting the
distance between the electron beams with respect to each other can
be provided. However, thereby a cross-over for the individual
electron beams might be generated which increases the
electron-electron interaction.
[0088] Generally, it might be desirable to combine advantages of
individual columns with large beam spacing and a beam array with
small beam spacing in one system by providing an adapting optics.
Thereby, according to some embodiments described herein, an array
of electron or charged particle emitters with a spacing sufficient
for integration of elements for individual beam control can be
provided. These individual electron beam optics might be
deflectors, lenses, stigmators, and the like. Thereby, according to
different embodiments, which can be combined with other embodiments
described herein, the electron emitter can be based on one or more
conventional thermal emitters, field emitters, or combined
thermal-field (Schottky) emitters. It may also be an array of photo
emitters.
[0089] Further, the multi-beam array may be formed by a separation
of one beam from one emitter tip into a plurality of beamlets, for
example by use of a grid aperture or a spot grid array. Thereby,
the space of the electron beams with respect to each other can
allow for individual electron beam optics for controlling the
electron beams individually. Further, according to some embodiments
described herein, an optical demagnification system can be
provided, as shown in FIG. 7. Thereby, the spacing of the beam
array is demagnified to the final requirements for simultaneous
inspection of one die or a small number of adjacent dies, for
example two or three dies. As a typical example, an optical system
with minimized (compensate) off-axis aberrations like a lens
doublet can be provided for the adapting optics. Thereby, according
to further embodiments, which can be combined with other
embodiments described herein, the lens system can be magnetic,
electrostatic or combined electrostatic-magnetic and can contain
two or more lenses.
[0090] Further, as exemplarily shown in FIG. 7, common electron
beam optics for global beam array manipulation are provided.
According to different embodiments, the common electron beam optics
may include a deflection *stem for alignment and/or scanning, lens
systems for focusing adjustments of the beam array, lens systems
for corrections, global stigmators, and the like.
[0091] Further, an array of common objective lenses, that is, a
common objective lens assembly can be provided. Thereby, the
objective lens assembly may have individual openings for each beam.
However, a common objective lens assembly is provided by the common
excitation, which focuses the individual electron beams
simultaneously.
[0092] Further examples of common objective lenses can include
magnetic lenses having a common excitation coil with common pole
pieces and an array of individual bores (openings), or common
electrostatic lenses having individual bores (openings) in a common
lens plate being on one potential. Thereby, according to different
embodiments, which can be combined with other embodiments described
herein, an electrostatic lens or an electrostatic lens component of
the common objective lens assembly can be used in an acceleration
mode or as a retarding electrostatic lens.
[0093] According to further embodiments, which can be combined with
other embodiments described herein, a multi-beam scanning electron
beam device as, for example shown in FIG. 7, includes a detection
system wherein an array of detectors is provided. Thereby, a
detector corresponding to each electron beam is provided. If the
electrostatic lens components 754 is provided as a retarding
electrostatic lens, the secondary electron beams are accelerated
and transferred through the objective lens and can for example be
detected on the detector 772. The detector 772 may be an array of
annular electron detectors above the objective lens. The secondary
electron beam, i.e., the signal beam may also be transferred to the
optical adapting system, which is in FIG. 7 a demagnification
system for the primary beams and, thus, a magnifying system for the
secondary beams. Thereby, the separation between the individual
beams is increased and in the case of a magnetic system the
secondary electron beams are separated from the primary beams by
the Lamor rotation of the secondary electron beams. Accordingly, a
further simplification of the design of the detector 774 can be
realized.
[0094] According to further embodiments, the detection can also be
improved by a further separation of the primary and the secondary
beam arrays. In this case, a beam separator based on a magnetic
field or a combined electrostatic-magnetic field can separate the
secondary beam array from the path of the primary beam array.
According to some embodiments described herein, an achromatic beam
separator as discussed e.g. with respect to FIGS. 2A-2D and can be
used. The "complete" separation simplifies design of the detector
and allows easier integration of elements for an energetic and/or
annular discrimination such as, for example energy filters and
spectrometers, and/or elements for annular multi-perspective
detection. According to further additional or alternative
implementations, the detection system may contain sector
field-based spectrometers, a retarding field spectrometer, lenses
for annular control, deflectors for alignment and selection and the
like. Thereby, according to typical embodiments described herein, a
common separation, filtering, alignment, annular control is
provided. Further, an array of detectors or individual detectors
for individual detection of each beam is provided.
[0095] Further embodiments, which can be combined with other
embodiments described herein, are described with respect to FIG. 8.
Thereby, a single emitter tip 102 is provided. If for example the
emission angle of the single emitter tip 102 is comparably small,
the separation provided by a grid aperture array or a spot grid
array can be relatively small. Thus, instead of an electron emitter
array with a spacing sufficient for individual beam control, an
emitter array with a small beam separation is provided.
Accordingly, for some embodiments, a magnification of the beam
spacing can be desired. As shown in FIG. 8, a magnification system
having lenses 727 and 725 is provided. As described with respect to
FIG. 7, several embodiments can be used for the adapting optics.
Typically, an optical system with minimized (compensated) off-axis
aberrations like a lens doublet can be provided. After this
increase of the beam separation, individual electron optical
elements 140 can be provided such that each electron beams 12, 13
and 14 can be individually controlled.
[0096] A common objective lens array focuses the plurality of
electron beams on the specimen 20. Thereby, a magnetic objective
lens component 752 and an electrostatic lens component 754 having
one or more electrode plates can be used. Accordingly, a common
objective lens assembly is provided. Thereby, the objective lens
assembly may have individual openings for each beam. However, a
common objective lens assembly is provided by the common
excitation, which focuses the individual electron beams
simultaneously. Further examples of common objective lenses can
include magnetic lenses having a common excitation coil with common
pole pieces and an array of individual bores (openings), or common
electrostatic lenses having individual bores (openings) in a common
lens plate being on one potential. Thereby, according to different
embodiments, which can be combined with other embodiments described
herein, an electrostatic lens or an electrostatic lens component of
the common objective lens assembly can be used in an acceleration
mode or as a retarding electrostatic lens.
[0097] According to yet further embodiments, it might be possible
to provide an electron beam array with a beam distance which allows
individual optical elements 140 such as lenses, multi-pole elements
for aberration compensation, deflection and/or stigmation control
as well as common electron beam optics 120. The common electron
beam optics 120 may include common scanning deflectors 724 and a
common beam control element 722 such as alignment deflectors,
stigmators or the like. As shown in FIG. 9, a common magnetic lens
assembly 752 and common electrostatic lens assembly 754 can be used
for focusing the primary electron beams on the specimen 20. A
detection can be realized with a detection array 772 having a
detection unit corresponding to the respective individual beams.
Thereby, the elements shown in FIG. 9 can be modified according to
the embodiments described herein, in particular with respect to
FIG. 7.
[0098] FIG. 10 shows a combination of embodiments described with
respect to FIG. 7 and embodiments described with respect to FIG. 1.
A multi-beam emitter 110 is provided. As an example, as shown in
FIG. 10, an array of individual emitters is provided. The electron
beams have a spacing with respect to each other such that
individual electron beam optics 140 can be provided. This can for
example be individual lenses or individual multi-poles. A beam
spacing adapting optics is provided by lenses 725 and 727.
Thereafter, the electron beam array passes through a common
achromatic beam deflector, which deflects the beam array of primary
beams and further separates the primary beam array and the
secondary beam array. Further, common electron beam optics 120 are
provided and the electron beam array is focused on the specimen 20
by the common magnetic lens assembly 752 and common electrostatic
lens assembly 754. The secondary beam array, that is the plurality
of signal beams, is separated from a primary beam array by a common
achromatic beam separator and the individual secondary beams are
detected by an array of detection units or individual detectors,
which are denoted by reference numeral 170.
[0099] FIG. 11A-11C show different embodiments for electron beam
array generation according to embodiments that can be used for the
high throughput tools described herein. FIG. 11A shows a multi-beam
emitter 1110A having a single emitter 1102 and an aperture grid
array, a lens and/or a lens array for generation of individual
beamlets. Thereby, the emitter 1102 has a small emission angle that
limits the separation of the beamlets. According to a further
embodiment, which is illustrated in FIG. 11B, a single emitter 1102
may have a larger emission angle such that a lens can be used to
guide the electron beam towards the aperture array. According to
yet other embodiments, individual emitters 1104 can be provided
such that an emitter 1110C can be provided. Thereby, also a spacing
sufficient for individual electron beam optics 140 can be
provided.
[0100] As described above, different options of generating the
multi-beam array can result in different distances between the
individual electron beams. Thus, the configuration of the optical
elements in the multi-beam system may depend on the type of
multi-beam emitter. In particular, the emitter spacing in the array
can influence the configuration of the further optics. Accordingly,
different embodiments may be provided. According to one embodiment,
a multi-beam high throughput tool such as a multi-beam scanning
electron beam device can include a multi-beam emitter formed by a
single emitter tip and a separation device like an aperture array
and/or a grid lens array, which form individual beamlets from the
single beam. Further, individual electron beam optics such as
lenses and multi-poles can be arranged in the array. The multi-beam
high throughput tool further includes common electron beam optics
such as deflectors for global alignment and scanning, common
stigmators and other elements described herein. A common magnetic,
electrostatic or combined electrostatic-magnetic grid lens array
for focusing the individual beams on the specimen is provided. The
multi-beam high throughput tool further includes a beam separation
means like a common beam separator or a common lens for introducing
a Lamor rotation. Further, a detection element including individual
detection for the secondary beams is provided and may for example
include and energetic and/or angular discrimination.
[0101] According to another embodiment, the above-described
embodiment may have been a beam spacing adapting optics
(magnification or demagnification) for the emitter array spacing in
order to adjust the spacing of the emitted beams to the objective
lens array spacing. Thereby, typically an optical system with
minimized off-axis aberration can be used. According to alternative
embodiments, the system may also include two adapting systems: one
for magnification of a spacing in order to allow easier integration
of the individual beam control components, and a further system for
demagnification of the beam spacing in order to adapt the objective
lens basing requirements.
[0102] According to alternative embodiments, which can be combined
with the above described embodiments, different kinds of multi-beam
emitters can be used according to the different embodiments
described herein. According to yet other modifications, a plurality
of individual emitters which can be further separated by grid one
or more aperture arrays can be used for generation of the
multi-beam array.
[0103] According to yet further alternative implementations, the
common objective lens assembly may have a smaller number of
openings than the number of individual beams in the array. Thereby,
two or more beams may share one opening in the common objective
lens array. However, it is preferred that at least two openings in
the common objective lens assembly are provided.
[0104] According to further alternative or additional
implementations, the double focusing bending element, such as a
bending sector, typically a spherical electrostatic sector
arrangement is provided. Typically, the individual beamlet
detectors can be positioned close to the focus of the sector in
order to avoid cross-talk between the individual beams. In order to
improve the space requirements, a scintillation detector with a
photomultiplier (PMT) and, for example, a light guide in between is
provided for each beam. Thereby, sufficient space for a PMT-array
can be realized. According to yet further embodiments, which can be
combined with other embodiments described herein, mechanical and/or
electromagnetic alignment for the individual secondary
electron-beamlets on the individual detector channels can be
provided. In light of the parallel detection of a plurality of
beamlets, it is further possible to have individual detection
electronics for each channel
[0105] According to some embodiments which can be combined with
other embodiments described herein, the systems for providing a
high throughput tool may typically be a low-voltage system, i.e.
having low beam energy on the specimen. This energy may for example
be in the range of 100 eV to 5 keV. Typically it is possible for
low-voltage beam energies to have the electrons traveling within
the column on a high beam energy, for example 8-10 keV or 7 to 15
keV. This beam boosts principle can reduce the electron-electron
interaction within one beamlet within the column in light of the
shorter flight. According to even further alternative or additional
implementations, the column components can be at ground potential
whereas the emitter and the wafer are at a high potential. Thereby,
the scan module, the beam separator and the bender can be at ground
potential. This simplifies in particular the common electron beam
optical elements.
[0106] A further embodiment of a multi-beam scanning electron beam
system is described with respect to FIG. 12. Thereby a spot grid
array 1210 is provided for the generation of the multi-beam. In the
gun condenser area the multiple beamlets are generated by a spot
grid array. This can be considered beneficial in light of the fact
that individual beams are emitted parallel to each other.
Accordingly, a beam tilt as described with respect to FIG. 2C
and/or a compensation of the achromatic separator as described with
respect to FIG. 2D can be omitted for a vertical objective lens
landing. Thereby, corresponding chromatic aberrations might be
further reduced.
[0107] In FIG. 12 common electron beam optical elements 120 such as
one or more common stigmators, one or more common beam alignment
elements, or one or more common beam rotating elements for rotating
the multi-beam array can be provided. Thereby, these components can
typically have one opening for trespassing of two or more electron
beams. Further, these common elements have a common control for
influencing the individual beams simultaneously.
[0108] FIG. 12 further shows a common achromatic beam separator
130, individual electron beam optical elements 140 and a common
objective lens assembly 150. Within FIG. 12, the beam path and the
corresponding elements of the secondary electron beam array are not
shown. However, it is understood that these components can be
provided according to any of the embodiments described herein, for
example with respect to FIG. 1 and/or FIG. 4.
[0109] According to embodiments described herein, the multi-beam
electron beam inspection device can be used for the design for
manufacturing (DFM) applications. According to a further
embodiment, the system includes an achromatic primary beam
separator for dividing beamlets of the primary beam array from
beamlets of the signal beams, i.e. the secondary beam array. As
described above, the secondary beam array might include secondary
particles, backscattered particles and other charged particles
which are released on impingement of the primary beams on the
specimen. Typically, for some embodiments, a beam boost can be used
for the beamlet configuration. That is, a high beam energy inside
the column is provided and the electrons are decelerated to the
final beam energy in the objective lens array. As described above,
electron-electron interaction can be reduced by providing a beam
boost, i.e. increased beam energy within the column.
[0110] Typically, if possible, the individual beams should travel
on different beam paths and the cross-over should be avoided in
order to minimise electron-electron interaction between the beams.
This is particularly relevant for high total beam currents, which
are typically used in light of the parallel imaging. The system
also includes an array of objective lenses. According to typical
implementations, this might be an electrostatic array, for example
in acceleration mode. This configuration allows for small
mechanical dimensions. Accordingly, a parallel imaging with a
plurality of beams is simplified. However, magnetic lenses or
combined electrostatic-magnetic lenses for simultaneously focusing
the multi-beam array can also be used.
[0111] According to embodiments described herein, there are common
electron beam optical elements for influencing two or more,
typically all beamlets. These common elements can, for example, be
a condenser lens such as a condenser lens for setting system
magnification, total current and/or the divergence angle of the
beamlets entering the objective lens array; common alignment and
stigmation components; and/or common scanning components (if
required). Further, common electron beam optical elements can
optionally be rotation means for rotating the beamlet array, for
example in an axial magnetic field.
[0112] The system further includes individual electron optical
elements for influencing each element of the beamlet array
individually. For example, the individual electron optical elements
might be elements for focusing, stigmation correction, objective
lens alignment, and/or beam scanning. The individual electron
optical elements generate typically transversal electrostatic,
magnetic or combined electrostatic-magnetic fields. These fields
might be generated, for example by magnetic, electrostatic or
combined electrostatic-magnetic multipole elements such as dipoles,
quadrupoles, octupoles or higher order elements according to the
requirements. Typically, for some embodiments the individual
influencing elements can be located near the objective lens.
Thereby, as further alternative or additional implementations,
single stage or multistage arrangements are possible. For example a
scanning element for individual beam scanning can be provided in
the form of a single state scanning element or a two-stage scanning
element.
[0113] As an example, an individual single stage scan deflector can
be located in front of, or be integrated into the bore of each
opening in the objective lens. Individual double stage scan
deflectors can be located in front of the objective lens array in
order to provide the pivot point inside the lens for improvement of
operations and telecentricity. Thereby a vertical landing angle or
a landing angle close to vertical can be provided.
[0114] According to some embodiments, which can be combined with
other embodiments described herein, a high brightness emitter with
large angular emission can be used to realize high currents in the
beamlets as well as in the overall system. For example, thermal
field emission cathodes such as TFE with large emitter curvature
radii (e.g. 0.5 .mu.m or larger or even 1 .mu.m or larger) can be
used. According to other embodiments, CFE, Schottky emitters, and
the like can be used.
[0115] According to yet further implementations, additionally or
alternatively a control electrode between the sample and the
objective lens for controlling the extraction field for the
secondary, i.e. released electrons can be provided. Thereby, as an
example, the control electrode has openings for the primary and
secondary beamlets. As a typical example, this electrode can be
integrated in the objective lens array. As a further typical
example, for electrostatic lenses, the control voltages might be
added on the voltage of the lens electrode being closest to the
specimen.
[0116] Multi-electron scanning electron beam systems described
herein can further include a signal path with individual detection
for each single signal beam, which is created by the primary beam
array. Thereby, it is further possible that the signal beamlets
penetrate the achromatic beam separator on individual traces.
Individual detectors or an array with individual detection areas
for each beam are located behind the beam separator. This can for
example be a scintillator-photomultiplier arrangement with
subsequence signal processing. Typically the signal processing can
also be provided individually for each beamlet.
[0117] According to yet further implementations, which can be
combined with embodiments described herein, an additional beam
deflection element can be located behind the beam separator in
order to increase the angles of separation between the primary beam
array and the secondary beam array. Thereby, a mechanical
arrangement of the detectors can be further simplified. Further, it
is easier to provide a focusing means for each of the signal
beamlets onto its corresponding detector if an additional beam
separation is provided. As an example, which can be implemented for
the embodiments described herein, the focusing means can be
arranged in front of, after or in the additional deflection means.
Typically, as described above, a double focusing additional element
like a spherical sector element can be provided. This element can
be electrostatic, magnetic or combined electrostatic-magnetic.
[0118] According to yet further embodiments, which can be combined
with other embodiments described herein, the system specifications
can include a current of the beamlets in a range of 10 pA to 10 nA,
for example 100 pA to 1 nA. Further, spot diameters used for
systems described herein may be in the range of 1 nm to 50 nm,
typically 1 nm to 20 nm.
[0119] Further options for systems described herein may include an
achromatic beam separator with a superimposed electro-magnetic
quadrupole, which might for example be generated by the octupole
element shown in FIG. 2B. This quadrupole may influence the
off-axis primary beamlets (in one direction) in such a way that all
beamlets will exit the objective lens array with vertical
incidents. Thereby, as described with respect to FIG. 2D, no
individual beam tilt might be required if non-parallel beamlets are
used in an achromatic beam separator. Thereby, chromatic
aberrations for the beams can be reduced and, accordingly, the spot
size and, thus, the resolution of off-axis beamlets can be
improved.
[0120] As a further option for systems described herein, a spot
grid array for generation of individual sources, i.e. individual
shaped beamlets which appear as individual sources on the sample,
may be used in the system. In light of the fact that individual
sources can be provided in a spot grid array an individual beam
tilt for having off-axis beamlets passing vertically through the
objective lens can also be omitted. As a further alternative,
individual emitter arrays may be applied as individual sources. For
example, micro field emitter arrays, TFE arrays or photo-cathodes
can be used. Thereby, as described above, generally for
multi-emitters as described herein, one emitter might generate two
ore more optical sources for the optical system.
[0121] Embodiments described herein also include methods for
generating a multi-beam array from a common emitter by placing an
aperture array in a divergent part of the emission. Further,
methods of influencing the beamlets such that each beam has a
specific performance with regard to its divergence angle, current,
tilt angle with respect to the optical axis of the entire system,
virtual tour size, and beam position with respect to the objective
lens array are provided. These methods are controlled by the
emission parameters, condenser lens excitation, and beam
influencing means, i.e. common electron optical elements,
individual being influencing means, i.e. individual beam optical
elements, and/or the operation condition of the achromatic beam
separator, typically a common achromatic beam separator.
[0122] Further embodiments relate to aligning each individual
beamlet to its corresponding objective lens position (opening) by
using the individual electron optical elements, which are provided
in front of or within the objective lens. Further, methods can be
directed to stigmation controlled by one or more stigmation
elements. Methods may also be directed to the determination of the
best focus, for example by a spot size or resolution measurements
using the signal of each signal channel. Further embodiments are
directed to methods for detecting the signal produced by each beam.
Thereby, the signal electrons entering the objective lens are
collected, the electrons are accelerated to high energies, for
example 5-20 keV, the signal electrode beamlets are separated from
the primary electron beam in the achromatic beam separator, and the
signal electron beamlets are guided to individual detectors with
subsequent signal channels. Typical embodiments of such
implementations include focusing the individual beamlets on the
individual detectors. Thereby, signal losses and cross-over between
the beams can be reduced or avoided.
[0123] According to yet a further embodiment, methods to
superimpose an electrostatic-magnetic quadrupole to an achromatic
beam separator (electrostatic-magnetic dipole) is provided. The
quadrupole can be aligned to the overall system optical axis,
whereby off-axis beamlets will be tilted (in one direction) for
vertical entrance into an objective lens array.
[0124] As describe above, embodiments can be directed to a
multi-beam scanning electron beam device having a column. The
device includes a multi-beam emitter for emitting a plurality of
electron beams, at least one common electron beam optical element
having a common opening for at least two of the plurality of
electron beams and being adapted for commonly influencing at least
two of the plurality of electron beams, at least one individual
electron beam optical element for individually influencing the
plurality of electron beams, a common objective lens assembly for
focusing the plurality of electrons beams having a common
excitation for focusing at least two of the plurality of electron
beams, and adapted for focusing the plurality of electron beams
onto a specimen for generation of a plurality of signal beams,
wherein the common objective lens has at least two openings for
trespassing of the plurality of electron beams, and a detection
assembly for individually detecting each signal beam on a
corresponding detection element. As further alternative or
additional implementations, the at least one common electron beam
optical element can be a common beam separator with a common
control for separating at least two of the plurality of signal
beams from the plurality of electron beams, the common electron
beam optical element can have one opening for trespassing of at
least two of the plurality of electron beams or for trespassing of
the plurality of electron beams, the common beam separator can have
one opening for trespassing of the plurality of at least two of
electron beams or for trespassing of the plurality of electron
beams, the common beam separator can be an achromatic beam
separator, and/or the achromatic beam separator can be adapted for
separating the plurality of electron beams and the plurality of
signal beams without generation of a cross-over of the plurality of
electron beams and/or the plurality of signal beams for
separation.
[0125] According to yet other additional or alternative
implementations, the device can include a quadrupole generation
element superimposing the achromatic beam separator and adapted for
generation of a quadrupole field for correcting the deflection
angle of off-axis electron beams, a double focusing beam bender, in
particular a hemispherical sector, wherein, for example, the double
focusing beam bender can have one opening for trespassing of the
plurality of beams, and/or a demagnifying or magnifying beam
spacing adapting optics.
[0126] According to yet even further additional or alternative
implementations, the common electron beam optical element can be
selected from the group consisting of: an alignment element, an
stigmation corrector, a scanning element, and rotating element for
rotating the plurality of electron beams, and/or the individual
electron beam optical element can be selected from the group
consisting of a focusing element, a stigmation corrector, an
alignment element, a beam tilt introducing element and a scanning
element. Further, according to other embodiments, which can be
combined with any of the embodiments described herein, the beam
spacing on the specimen between adjacent beams can be in a range of
0.5 to 5 mm, in particular 1.5 mm to 3.5 mm, more particularly 2 mm
to 3 mm, the individual electron beam optical element can be
position adjacent to or within the common objective lens assembly,
and or means for accelerating the plurality of electron beams to
high energies between the multi-beam emitter and the objective
lens, in particular to energies of 2 keV to 20 keV, and means for
decelerating the plurality of electron beams before impingement on
the specimen can be provided.
[0127] According to yet other alternative or additional
implementations, the device may include focusing means for focusing
each of the plurality of signal beams on the corresponding
detection element, multi-beam emitter can be a spot grid array
having individual emitters for each of the plurality of electron
beams, the device can be adapted for avoiding a cross-over in the
column, and/or the common objective lens assembly can be an
electrostatic lens assembly, in particular in acceleration
mode.
[0128] According to other embodiments, a method of operating a
multi-beam scanning electron beam device for generation of an image
of a wafer including two or more dies is provided. The method
includes scanning a first region of a first die of the two or more
dies for generating an image of the first region, scanning a second
region of a second die of the two or more dies for generating an
image of the second region, combining the image of the first region
and the image of the second region to an image of a virtual die.
Thereby, as one optional implementation the virtual die can be
combined by images of regions of three or four dies of the two or
more dies.
[0129] According to yet other embodiments, a method of operating a
multi-beam scanning electron beam device having at least a first
and a second electron beam for generation of an image of a wafer
including at least one die, is provided. The method includes
scanning a non-overlap first region of the die with a first
electron beam current of the first electron beam for generating an
image of the first region, scanning a non-overlap second region of
the die with a second electron beam current of the second electron
beam for generating an image of the first region, and scanning an
overlap region between a scanning area of the first and the second
electron beam with the first beam having an first overlap depending
beam current function having electron beam currents being smaller
than the first electron beam current and with the second beam
having an second overlap depending beam current function having
electron beam currents being smaller than the second electron beam
current. According to additional implementations, the first current
and the second current can be similar and the first overlap
depending beam current function and the second overlap depending
beam current function are similar and/or the first and the second
overlap depending beam current functions can be a linear
function.
[0130] According to yet other embodiments, a method of operating an
achromatic beam deflector for charged particle beams can be
provided. The achromatic beam deflector having an optical axis. The
method includes providing a deflecting electrostatic dipole field,
providing a deflecting magnetic dipole field, superimposing a
quadrupole field to the magnetic dipole field and the electrostatic
dipole field, wherein the electrostatic dipole field and the
magnetic dipole field are adjusted with respect to each other to
provide an achromatic beam deflection, and wherein the quadrupole
field is adjusted to correct for a beam tilt of off-axis charged
particle beams. According to typical implementations, the charged
particle beam can be deflected for an angle of between 0.3.degree.
and 7.degree., the quadrupole field can be aligned to the optical
axis of the achromatic beam deflector, an off-axis beam of a
multi-beam array can be corrected and/or a correction can be done
along one direction.
[0131] While the foregoing is directed to embodiments of the
invention, other and further embodiments of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
* * * * *